Abstract

Predictive or presymptomatic genetic testing enables individuals at risk for a hereditary late‐onset disease to learn about
their genetic status before symptoms have appeared. The predictive testing protocol for Huntington disease (HD) safeguards
the interests of test candidates and has served as a model for other diseases. Most people seen for genetic counselling regarding
HD are the asymptomatic children of an affected parent. Predictive testing provides the opportunity to get relief from the
anguish of being at risk, to have prenatal tests or preimplantation genetic testing in order to have children free of the
disorder, and to make informed plans for the future regarding marriage, education, professional career and finances. The common
experience has been that tested individuals found relief from their prior psychological distress and that they benefited psychologically.
Having children proved to be an additional stress factor for partners.

Key Concepts

Predictive testing provides the opportunity to get relief from uncertainty and prepare better for the future.

Preimplantation genetic testing enables couples to have a pregnancy without the burden of termination after an unfavourable
prenatal test result.

At 55 years of age and being not symptomatic, there is still a 25% empirical chance of being a carrier of the Huntington's
gene.

The Huntington disease CAG repeat length accounts for roughly 50–77% of the variation in the age of onset.

Predictive testing requires informed consent by the individual at risk and the provision of psychological support.

Predictive testing for adult‐onset disorders without treatment options should not be offered to children and adolescents.

Counselling test candidates at 25% risk to get Huntington disease requires a family system approach.

The predictive test candidate's beliefs about causation and emotional, social and cultural issues may affect the perception
of the information that is given in genetic counselling.

Figure 1. Exclusion testing in Huntington disease (HD). In this family, the HD gene is associated with marker genotype H. Thus, if a person (or pregnancy) at 25% risk has also inherited genotype H (a), he/she will be at high risk of developing HD (50%, the same as for the intervening parent), whereas if a person has inherited genotype A (b), derived from the unaffected grandparent, the risk will be low.

Borry P, Shabani M and Howard HC (2014) Is there a right time to know? The right not to know and genetic testing in children. The Journal of Law, Medicine & Ethics 42 (1): 19–27. DOI: 10.1111/jlme.12115.